1. Field of the Invention
This invention relates to integrated circuit structures. More particularly, this invention relates to the processing of exposed surfaces of a low dielectric constant carbon doped silicon oxide dielectric material in a manner which will protect the low dielectric constant carbon doped silicon oxide dielectric material from damage.
2. Description of the Related Art
In the construction of integrated circuit structures, dielectric materials such as silicon oxide (SiO.sub.2) have been conventionally used to electrically separate and isolate or insulate conductive elements of the integrated circuit structure from one another. However, as the spacing between such conductive elements in the integrated circuit structure have become smaller and smaller, the capacitance between such conductive elements through the silicon oxide dielectric has become of increasing concern. Such capacitance has a negative influence on the overall performance of the integrated circuit structure in a number of ways, including its effect on speed of the circuitry and cross-coupling (crosstalk) between adjacent conductive elements.
Because of this ever increasing problem of capacitance between adjacent conductive elements separated by silicon oxide insulation, as the scale of integrated circuit structures continues to reduce, the use of other insulation materials having lower dielectric constants (k values) than conventional silicon oxide (SiO.sub.2) has been proposed. One such class of material is a carbon doped silicon oxide material wherein at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by one or more organic groups such as, for example, an alkyl group such as a methyl (CH.sub.3 --) group. Such low k carbon doped silicon oxide dielectric materials have dielectric constants varying from about 2.5 to about 3.5 and are, therefore, of great interest as low dielectric constant substitutes for the conventional silicon oxide (SiO.sub.2) insulation material.
The substitution of one or more organic groups for some of the oxygen atoms bonded to the silicon atoms in a silicon oxide dielectric material has a beneficial effect in the lowering of the dielectric constant of the carbon doped silicon oxide material, therefore lowering the capacitance between conductive elements separated by such dielectric material. However, it has been found that the bond formed between the silicon atoms and the organic groups is not as stable as the silicon-oxygen bond found in conventional silicon oxide (SiO.sub.2) materials.
In particular, for example, unprotected surfaces of such a low k carbon doped silicon oxide dielectric material may be exposed to oxidizing or "ashing" systems, which are used to remove a photoresist mask from the layer of low k carbon doped silicon oxide dielectric material, after formation of openings, such as vias, therein. It has been found that the ashing process results in damage to the bonds (cleavage) between the organic groups and the silicon atoms adjacent the surfaces of the layer of low k carbon doped silicon oxide dielectric material exposed to such an ashing treatment. This cleavage of the carbon-silicon bonds, in turn, results in removal of such organic materials formerly bonded to the silicon atoms along with the organic photoresist materials being removed from the integrated circuit structure. The silicon atoms from which the organic groups have been cleaved, and which are left in the damaged surface of low k carbon doped silicon oxide dielectric material, are in a highly reactive state and become water absorption sites if and when the damaged surface is exposed to moisture. The damaged low k carbon doped silicon oxide dielectric material, and its resultant susceptibility to moisture may be illustrated by the following equations: ##STR1##
This absorption of moisture by the damaged low k carbon doped silicon oxide dielectric material, results in hydroxyl bonding to the reactive silicon atoms left from the cleavage of the carbon-silicon bonds in the damaged surfaces of the low k carbon doped silicon oxide dielectric material. This silicon-hydroxyl bond is not a stable bond, and subsequent exposure to heat, e.g., during subsequent processing such as annealing, can result in cleavage of the silicon-hydroxyl bond, thereby causing water vapor formation which, for example, can interfere with subsequent filling of a via/contact opening or a damacene trench with metal filler material.
The upper surface of the low k carbon doped silicon oxide dielectric material can be protected from such attack during removal of the resist mask by provision of a protective layer, e.g. silicon oxide over the upper surface. However, damage caused by ashing and the use of solvent additionally causes physical damage to any carbon doped silicon oxide material which is exposed in walls of vias or contact openings, resulting in cracked, degraded, bowed, and porous insulating material in the walls of vias or contact openings. The pores in the walls of vias or contact openings can present further problems by retaining solvent within pore cavities as well as retaining, in pore cavities, destructive gases produced during one or more subsequent metal deposition steps. The physical damage to the insulating material which forms the walls of vias or contact openings cause the subsequent metal deposition step to be unreliable; and the presence, in the pore cavities, of gases produced during metal deposition steps result in a degradation of the metal/metal nitride properties.
In copending U.S. patent application Ser. No. 09/281,514 entitled "PROCESS FOR TREATING DAMAGED SURFACES OF LOW DIELECTRIC CONSTANT ORGANO SILICON OXIDE INSULATION MATERIAL TO INHIBIT MOISTURE ABSORPTION", filed Mar. 29, 1999 and assigned to the assignee of this application, it is proposed to treat such damaged sidewalls with either a hydrogen plasma or a nitrogen plasma. Such a treatment with a hydrogen or nitrogen plasma causes the hydrogen or nitrogen to bond to silicon atoms with dangling bonds left in the damaged surface of the low dielectric constant organo silicon oxide insulation layer to replace organo material severed from such silicon atoms at the damaged surface. Absorption of moisture in the damaged surface of the low dielectric constant organo silicon oxide insulation layer, by bonding of such silicon with moisture, is thereby inhibited.
However, it would be desirable to provide a method for processing a low k carbon doped silicon oxide dielectric material, located on an integrated circuit structure, in a manner which will protect surfaces of the low k carbon doped silicon oxide dielectric material exposed by formation of one or more vias therein from being damaged during removal of the etch mask.